Magnetic separator

ABSTRACT

A magnet assembly for use such as in a magnetic separator having main magnetic elements with aiding magnetic elements disposed therebetween and having their polarities directed transversely thereto such that increased lines of magnetic flux, increased effective pole area, decreased gap length, improved repulsion of flux leakage both at the edges of the main magnetic elements and between the sides of adjacent main magnetic elements, and reduced flux leakage at the rear face of the main magnetic elements is achieved.

O Umted States Patent [1 1 [111 3,737,822 Buns et al. 1 June 5, 1973 s41 MAGNETIC SEPARATOR 3,365,599 l/l968 Brezezinski et al.....; ..s3s/3o4 x 3,454,913 7 1969 l I tal .335 306 [75] Inventors: Harold W. Buns, Hales Corners; I me son 6 I Donald Morgan, Milwaukee, primary Examineriqggrge Hams both of Attorney-Axel A. Hofgren, Ernest A. Wegner, [73] Assignee: Magnetics International, lne., Maple H J Stellman et Heights, Ohio 57 STRACT AB [22] Filed: Mar. 29, 1972 l 1 A magnet assembly for use such as in a magnetic [21] Appl' 239,098 separator having main magnetic elements with aiding magnetic elements disposed therebetween and having Related Application their polarities directed transversely thereto such that [63] Continuation-impart of Ser. No. 45,095, June 10, increased lines of magnetic flux, increased effective 3, pole area, decreased gap length, improved repulsion of flux leakage both at the edges of the main magnetic [52] US. Cl ..335/304, 209/219 elements and between the sides of adjacent main mag- [51] Int. Cl ..li01l7/02 netic elements, and reduced flux leakage at the rear [58] Field of Search ..209/2l9, 223, face of the main magnetic elements is achieved.

[56] References Cited 12 Claims, 11 Drawing Figures UNITED STATES PATENTS 2,895,092 7/1959 Cluwen "335/304 Pm-id June 5,191;

4 Sheets-Sheet 1 T R A R w R P Patented June 5,19% 3,737,822

4 She ets-Sheat 2 Patented June 5, 1973 I 3,737,822

4 Sheots-Shaot'4.

FIG. 9

" NoLMAeNEfic (AM ERIAL MAGNETIC MATERIAL FIG. n

MAGNETIC SEPARATOR CROSS REFERENCES This application is a continuation-in-part of application Ser. No. 45,095, filed June 10, 1970, now US. Pat.

BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relates to magnet assemblies and in particular to magnet assemblies for use inmagnetic separators and the like.

2. Description of the Prior Art In one improved form of magnetic separator as shown in Buus et a1. Pat. No. 2,992,736 owned bythe assignee hereof, a plurality of permanent magnets are mounted in a cylindrical shell with magnet pole pieces disposed between the magnets to provide a flux extending outwardly through, the shell for magnetically attracting magnetic solids and the like, such asin slurries,

to the cylindrical drum surface thereby to separate such solids from the slurry for suitable delivery to'a discharge means. The magneticseparator of said Buuset alpatent provides high efficiency in the separating operation with effectively minimized permanentmagnet material in the assembly.

SUMMARY OF THE INVENTION The present invention comprehendsan improved magnet assembly such asfor use in such a magnetic separator which provides further improved efficiency in the utilization of the magnetic material and imtOl. I 2 More specifically, theinvention comprehendsproviding aiding magnetic elements or poles intermediate proved separating functioning of the magnetic separa work surface of the assembly and, further, to add to the magnetomotive force at the back or inner surface of the assembly to increase the useful flux produced externally of the outer working surface of the assembly.

BRIEF DESCRIPTION OF THEDRAWING Other features and advantages of the invention will be apparent from the followingdescription taken in connection with the accompanying drawing wherein:

FIG. 1 is a vertical cross-sectional view illustrating a magnetic separator utilizing a magnet assembly of the prior art; I

FIG. 2 is a vertical cross-sectional view illustrating a cylindrical drum type magnetic separator utilizing an axial pole magnet assemblyembodying the invention;

FIG. 3 is a diagrammatic illustration of a magnetic separator having a magnet assembly of the present in- FIGS. 5 and 6 hereof in separating magnetizable and non-magnetizable materials; I

FIG. 8 is-a vertical cross-sectional view illustrating a magnetic separator of the cylindrical drum type form of that of FIG. 2 but utilizing a different embodimen the primary magnetic'elements or-poles. Inafirst em:-

bodiment, the external flux isproducedbetween the opposite poles of the main magnets,xand" the aiding magnetsare located onlyv at the outerextremitiesot the main magnetswhile-in a-second embodiment, the external ffluxis produced between opposing poles ofa'djacent main magnets, and-the aiding magnets are substantially coextensive with the .mainmagnets. In both embodiments, pole pieces provide low reluctance flux paths between the poles of themainmagnetsfor'direch ingthe flux through the aiding magnets; The aidingpoles'in both embodiments providezimpro'ived magnetomotive force resulting in increased lines of fluxuseful in the magnetic separati'ngope'rationr. I

' In the first embodiment, the aiding poles effectivelyincreasethe pole area andreduce the gap between the poles to provide improved-effective separation. The aiding poles further. repel ineffective leak lines -at the.

front edges of the poles. Further, by increasing the desired flux at the front or 'working surfaceof the magnet of the magnet assembly of the invention;

FIG. 9 is a vertical cross-sectional view'of a magnetic separator of the pulley type form of that of FIG. 5 but provided'wi'th the embodiment of the magnet assembly of the invention shown in-FIG. 8;

FIG. 10 is a sectional view taken substantially along the line 10l0 of FIG. 9; and t FIG. 11 is a sectional view taken substantially along I line 11-ll of FIG. 1

assembly, a reduction in'.-the undesirable leakageflux at the back of the assembly is obtained. The"-utilization'of the disclosed aiding poles permits the'useof" an increased amount of magnet material in thelassemblywhile preventing an increasein the'gapbetweenthepoles. r v f In'the' second embodiment, the-aiding magnets coextend intermediate of adjacent main magnets'and havetheir polarities directed to repel ineffective leakage'flux both along the side of themain magnetsand between the sides of adjacentm'ain magnetstoward'the outer DESCRIPTION OF THE PREFERRED EMBODIMENT In the exemplary embodiment of the invention 'as disclosed in FIGS. 2-5 of the drawing, a drum type magnetic separator generally designated 10 is shown to include a drum 11 having a magnet assembly generally designated 12 mounted on the axial shaftl3. The'magnet assembly is disposed within a cylindrical outer shell 14 and-serves to provide magnetic flux outwardly of the shell'attracting magnetizable solids from a slurry to the surface of the drum for effectively separating themagnetic solids from nonmagnetic solids of the slurry. The drum may be rotated by suitable electric motor'drive 15."The magnetic separator may be mounted on a suitable frame 16.The drum 11 may be similarly utilized for separating magnetic solids from a dry mixture, as

shown-in FIG. 4 wherein the dry materialis fed to the magnetic separator by means of ahopper 17. The drum may be similarly rotatedbyan electric drive generally designated 18.

The magnet assemblies of the prior art utilize stacked permanent magnets such as magnets 19, as shown in FIG. L SuitabIe soft iron pole pieces 20 are provided intermediate the end-to-end arranged magnets. 'For a complete description of such a magnet assembly, reference may be had to the above identified Buus et al. Patent No. 2,992,736. As discussed above, the Buus et al. magnetic separator provides an excellent highly efficient separator device. The present invention, however, comprehends a further improved modification of such a magnetic separator providing increased efficiency in the use of the magnetic material by an improved circuit configuration producing increased flux strength and thereby improved separation functioning. lllustratively, the present invention comprehends an arrangement wherein an increase in the flux strength of approximately percent over that of said Buus et al patent structure is realized.

More specifically, as shown in FIG. 2, magnet assembly 12 includes a plurality of stacked magnets, such as magnets 19a, 19b, 19c and 19d. The magnets are arranged in magnetic opposition as indicated by the arrows 21 whereby theconfronting ends of magnets 19a and 19b comprise the south pole ends of these magnets, the confronting ends of 19b and 190 comprise north pole ends of these magnets, and the confronting ends of 190 and 19d comprise south pole ends of these magnets. The magnets are secured in the assembly by means of holding plates 22a, 22b, 22c and 22d of nonmagnetic material extending between a pair of end plates 23. Triangular shaped pole pieces 24a, 24b and 240 are disposed between the respective confronting magnet ends and end pole pieces 25a and 25b are provided at the opposite ends of the magnet assembly. The magnets may be formed of suitable non-metallic material, such as iron oxide, and at least one metal of the group consisting of strontium, barium and lead. Illustratively, the magnets may be formed of barium or strontium ferrite material of well-known composition. The pole pieces may be formed of mild steel and the like.

To provide the improved flux strength, aiding poles 26, 27, 28, 29 and are provided in outer recessed corners of the magnets. The aiding poles may be formed of magnetic material similar to the magnetic material of magnets 19a 19d and extend across the outer portion of the gaps between the confronting magnet ends as well as outwardly from the magnet assembly ends adjacent pole pieces 25a and 25b. Each of the aiding poles inwardly abuts the adjacent pole piece to provide a continuation of the magnetic circuit therefrom to the radially extending outer surface of the assembly. Thus, aiding poles 26, 28 and 30 have their north ends disposed radially outwardly and aiding poles 27 and 29 have their south ends disposed radially outwardly.

The aiding poles increase the magnetomotive force produced in each magnet unit and thus develop an increase in the lines of flux L generated radially outwardly from the assembly for use in the magnetic separation operation. By extending the aiding poles circumferentially beyond the spaces between the pole ends as occupied by the pole pieces, an increase in the effective pole area is provided reducing the effective gap between the poles so as to provide improved magnetic separation. The aiding poles further repel leakage flux at the pole edges such as pole edge 31. Still further, in such magnetic assemblies some flux is lost at the radially inner portion of the assembly illustrated by flux line 32 in FIG. 2. The use of the aiding poles herein effectively minimizes the effect of such leakage at the back of the assembly by virtue of an attraction force produced on the leakage flux. Further, in effect, the aiding poles reduce the reluctance at the outer surface of the assembly as compared to the back or inner surface so as to provide an improved flux concentration at the radially outer working surface.

In illustrating the invention, the improved aiding pole structure has been shown as used in conjunction with a magnetic separator assembly somewhat similar to that of the Buus et al. Patent No. 2,992,736. As will be obvious to those skilled in the art, the inventive concept is applicable to other pole arrangements and magnet assembly designs. In the illustrated embodiment, the magnet assembly is stationary while the drum is rotatable. As will be obvious to those skilled in the art, the invention is applicable to such magnet assemblies where the magnet rotates as well as with the stationary arrangement. Further, the invention has been illustrated in connection with a magnet assembly utilizing five poles. It will be obvious to those skilled in this art that any number of poles may be utilized in the assembly in conjunction withthe aiding pole structure dis cussed above.

Further illustratively, the aiding pole structure concept may be utilized with a radial pole pulley structure such as structure 32 of FIG. 5. Such a structure is generally shown in Buus et al. Patent No. 2,992,733, reference to which may be had as to a detailed disclosure of the pulley assembly. Thus, as shown in FIG. 7, the pulley assembly comprises a cylindrical magnetic structure over which a belt 33 carrying material to be separated is passed. As the belt moves about the magnetic separator, the magnetizable material 34 is retained on the belt to a position adjacent the bottom of the pulley whereas the nonmagnetizable material 35 falls from the belt at the outermost portion of the turn thereof about the pulley. Thus, the two different types of material may be collected in suitable subjacent hoppers 36 and 37.

Briefly, as shown in FIG. 5, pulley 32 includes a shaft 38 coaxially carrying a tubular support 39 mounting a plurality of annular magnets 40 and 41 which may comprise magnets stacked parallel to the axis of shaft 38. Intermediate magnets 40 and 41 is a dual pole piece 42. At the outer end of magnet 40 is provided a pole piece 43 and at the outer end of magnet 41 is provided a pole piece 44, the pole pieces 43 and 44 being mounted to the shaft 38 by means of end hubs 45. The magnet assembly may be enclosed in a non-magnetic tubular cover 46.

The present invention, in one embodiment, comprehends providing aiding poles at the outer corners of the magnets 40 and 41 to provide similarly improved functioning as provided with magnet assembly 12. Thus, as seen in FIG. 5, an. aiding pole 47 may be provided at the confronting ends of magnets 40 and 41 radially overlying pole pieces 42. Aiding pole 48 may be provided at the outer end of magnet 40 overlying pole piece 43 and an aiding pole 49 may be provided at the outer end of magnet 41 overlying pole 44. The aiding poles herein may comprise annular poles having suitable orientation to continue the path of flux F generated outwardly of cover 46 for effecting the desired magnetic separation functioning. Thus, where the confronting ends of magnets 40 and 41 comprise south poles, aiding pole 47 is arranged to have its radial outer end define the south pole thereof. Aiding poles 48 and 49 are reversely arranged to complete the flux path.

Thus, magnet assembly 32 functions similarly to magseparator functioning by means of an improved flux generation and distribution. Each of the features discussed above relative to the aiding poles-of assembly l2 is applicable to the aiding poles of assembly 32.

Turning now to FIGS. 8.1l, a second embodiment of applicants invention is shown in which the aiding magnets of the first embodiment have been proportionately increased in size and strength to become the main mag.- nets, i.e., the magnetsproviding the greatestportion of the total magnetomotive force of the assembly, while the main magnets of the first embodiment have been proportionately reduced to become aiding magnets. Converse to the respective polarity directions or the main and aiding magnets of the illustrations of the first embodiment, the aiding magnets have their polarities tangentially directed, while the polarities of the main magnets are radially directed. The second embodiment may be utilized in the same manner as the first embodiment in an axial pole drum structure similar to that of FIG. 2, as shown in FIG. 8, or in a radial pole pulley structure similar to that of FIG. 5, as shown in FIGS. 9-11. The inventive concept is, of course, applicable to other pole arrangements and magnet assemblydesigns.

Specifically, referring to FIG. 8, an axial pole magnet assembly, generally designated by reference numeral 52, illustrates the second embodiment of applicants invention as used in a cylindricaldrum typeseparator. Briefly, magnet assembly 52 includes first, second and third main magnets 54a, 54b, ,and'54c, respectively, extending from an outer working surface 56 toward an inner surface 58 and magnetized in a substantially radial direction with respect to cylindrical axis 60. As indicated by the arrows, adjacent main magnets have their polarities substantially .oppositelyldirected. Main magnets 54a and 540 have their polarities, from north poles 62a and 620 to south :poles .64a' and 64c,

ties of the aiding magnets are directed to provide a magnetomotive force additive to the magnetic flux 70 between the first pairs of opposing main magnet poles 54 at inner surface 58 through their respective pole pieces 68-to increasethe magnetic flux 66 produced externally of outer working surface 56. The aiding mag-.

netsextend inwardly beyond the poles of main magnets 54 to present pole faces 65 spaced therefrom to control the flux distribution such that the magnetic flux from the main magnets is in alignment with the flux produced by the aiding magnets and confined within the space defined by the aiding magnets. The pole pieces provide a low reluctance path for the flux between the poles of the main and aiding magnets and, as previbusly stated, present a face directed to further align and concentrate the main magnetic flux with the magnetic flux produced by the aiding magnets.

A leakage flux is normally produced between the sides of adjacent main magnets, and the aiding magnets extend to the outerworking surface 56 intermediate of the main magnets and have their polarities directed thereat to oppose this leakage flux, thereby repelling the leakage flux to, again, increase the magnetic flux 66 produced externally of outer working surface 56.

At either 'end of the assembly are providedterminal aiding magnet means comprising aiding magnets 74, ,each having one pole 76 adjacent outer sides 78 of the end or terminal main pole pieces 68a and 680 and another pole 80 spaced therefrom with an aiding pole piece 82 forming an' extension thereof. Terminal aiding magnets 74 have their polarities directed substantially transverse 'to the terminal main magnets 54a and 540 for providing a magnetomotive force additive to the magnetic flux between the opposing poles of the termi- 'nal main magnets through the terminal main pole pieces 68a and 680 and terminal aiding pole pieces 82,

respectively, directed radially out-ward from cylindrical axis 60,,while main magnet 54b,adjacenttmain magnets 54a and 540, has its polarity, from north pole 62b to south pole 64b, directed radially inward toward-axis60. Thus, a first pair of opposing poles ;of adjacent main magnets .are located adjacent one another at .inner surface 58 and the second .pair of opposing poles of adjacent main magnets are located ,adjacentone another at theouter working surface '56of the assembly. This configuration resultsin the production .of magnetic :fluxexternal of outer working-surface 56 between the second pair of opposing polesof the main magnets, diagram- .matically indicated :by .dashed lines .66.

Forming an extension; of the rnain magnets at poles 62a, 64b and 62c adjaeent inner surface 58 are pole pieces 68a, 68b and 68,c,'- respectively, which :maybe made ofmagnetically permeable mild steelor any other suitable ferromagnetic .material. The .pole pieces are contiguous withthe-main polesand extend inwardly toward inner surface 58;an d have sides 63 facing substantially transverse to'the main magnets to 'direc t themagnets, as indicated by dashed lines 70,-as will be explainedin more detail hereinafter. I

Respectively intermediate of main pole pieces 68a and 72b, which maybe eomprised'ofstacked ceramic netic flux between paijrsjof opposing ,poles'of adjacent .main magnets throughjthe intermediate ,aiding magand68b, and.68b and 68eare aiding magnetmeans 572a as schematically indicated by dashed lines 84, to increase the magnetic flux produced externally of outer working surface 56 between the main poles 64a and 640 and aiding pole pieces 82, as schematically indicated by dashed lines 86. The terminal aiding magnet means extend toward the outer working surface and further increase magnetic flux 86 by repelling leakage both along the sides of the main magnets and between the aiding magnet pole piece and the side of the end main magnets, as discussed above. The terminal aiding magnet pole pieces 82 further provide a low reluctance path for the flux between the opposite poles of the end main magnets.

Further illustratively, the second embodiment of applicants invention may be utilized with a radial pole pulley structure such as magnet assembly 88 of FIGS.

9-11. The basic pulley structure is similar in structure bly 52 of FIG. 8 will be given the same reference numetals.

Briefly, an aiding magnet 72 is disposed intermediate of .two mainmagnets 54 and their respective associated pole pieces 68 and terminal aiding magnets 74 with their respectiveassociated aiding pole pieces 82, are

located at both ends of the assembly and flanking main magnets 54. Due to the even number of main magnets in assembly 88, the respective polarities of terminal aiding magnets 74 at either end of the assemblyare of like direction. If there were an odd number of main magnets in the assembly, as shown in the assembly of FIG. 8, the polarities of the terminal aiding magnets at either end of the assembly would, of course, be oppositely directed. Each of the features discussed above relative to the arrangement of main magnets, main magnet pole pieces, aiding magnets, and aiding magnet pole pieces of assembly 52, is applicable to the like elements of assembly 88. That is, magnetic assembly 88 functions in a manner similar to that of magnetic assembly 52 to provide a magnetic separator having an improved flux generation and distribution.

However, the radial pole pulley structure of FIGS. 9-11 is different from that of FIG. in that two different magnetic zones are provided along the circumference of the pulley assembly 88: a separation zone 92,

which is magnetically the strongest portion of stationary magnetic assembly 88, to separate magnetic materials from nonmagnetic materials by attracting the magnetic materials to a rotating drum 96, and a transporta tion zone 94 which produces a magnetic field weaker than that of the separation zone but of sufficient strength to hold the attracted magnetic materials to the rotating drum 96 to carry them beyond a division vane 98 for discharge. Although FIG. 10 shows the use of assembly 88 in an overfeed configuration, the assembly may also be used in an underfeed operation, with the stronger separation zone lower than the transportation zone to lift the magnetic materials from a conveyor passing under the drum with the attracted material then being carried through the transportation zone and over the top of the drum for discharge.

As illustrated in FIG. 9, the respective pole pieces 68 I for the two main magnets 54 function as back plates to which the main magnets are mounted, with the back plates, in turn, being secured to axle 60 by a suitable securing means 100. Pole pieces 68 have two portions: a first portion 68' for mounting the main magnets in the separation zone and a second portion 68" for mounting the main magnets in the transportation zone. Pole piece portion 68' is in the form of a substantially straight elongated bar extending along a cord of the cylindrical assembly, while pole piece portion 68" is in theform of a curved bar generally conforming to the curvature of cylindrical drum 96. One end of pole piece portion 68" is secured to the inner side of pole piece portion 68' such that the end face of pole piece portion 68' forms a continuation of the outer surface of pole piece portion 68".

The main magnets 54 have two portions of different configurations respectively corresponding to the pole piece portions 68' and 68" to which they are mounted. As shown in FIG. 9, a portion 54' of the main magnets is mounted directly to pole piece portions 68' and is formed of stacked magnet wafers of various depths with the deepest portion being generally at a radius through axle 60 and normal to pole piece portion 68'. The depth of the stack decreases in both directions away from this radius so that the pole faces adjacent the outer working surface conform generally to the cylindrical curvature of drum 96. The depth of the stack decreases more rapidly in a direction away from the radius toward the transportation zone than toward the separation zone to underlie a part of a portion 54 of the main magnets, part of which is mounted to pole piece portion 68 and a part of which extends toward the separation zone to overlie the main magnets 54'.

Main magnet portion 54' may comprise a plurality of stacked ceramic magnetic wafers which are placed end-to-end to form a portion of an annulus having an outside surface generally conforming with the cylindrical surface of drum 96 and forming a continuation of the outer surface of the mainmagnet portion 54' in the separation zone. The portion 54" of the main magnets in the transportation zone is of the same polarity of the portion 54 of the main magnets in the separation zone and may be considered as forming a magnetically weaker radial extension thereof into the transportation zone.

The aiding magnets are also in two portions of similar configuration to that of the two portions of the main magnets. One portion of the aiding magnets is mounted to a suitable high reluctance mounting means substantially extending along pole piece portion 68' in the separation zone which, in turn, is mounted to the securing means 100, and a second portion is mounted to a curved mounting means portion 102" which is secured to, and of like suitable material to that of mounting means portion 102 and which extends substantially along the inner surface of pole piece portion 68" in the transportation zone. The two portions of the aiding magnets extend outwardly from their respective mounting means toward the outer working surface and are generally coextensive with the main magnets in that direction.

The basic structure of aiding poles interposed between main poles with pole pieces for the main poles provided at the inner surface of the assembly is substantially the same as that shown in FIG. 8. FIG. 10 shows a view of a section generally taken along line 10-10 through the assembly in the separation zone of FIG. 9 and it is seen to be very similar to the construction shown in FIG. 8. FIG. 11 is a sectional view taken along line 11-11 of FIG. 10 through the magnets in the transportation zone and shows that the basic structure of aiding poles interposed between main poles is maintained in the transportation zone. It should be appreciated that many other configurations within the scope of applicants invention are possible. For example, the basic structure of main magnets, aiding magnets and pole pieces could be utilized where the assembly comprises only one main magnet provided with terminal aiding magnets on opposite sides thereof or even in an assembly comprising only one main magnet provided with a terminal aiding magnet on only one side thereof.

Further, magnet assemblies 12, 32, 52 and 88 are overall dimensionally similar to the magnet assemblies of the Buus et a] patents identified above. Thus, the magnetic assemblies may be substituted in the magnetic separators disclosed therein for improved magnetic separation functioning in the apparatuses of these patents so that the arrangement of the magnet assemblies 12, 32, 52 and 88 avoids obsolescence of existing magnetic separator structure while providing for substantially improved performance thereof by direct substitution in such existing structures.

Although the confronting surfaces of adjacent elements of the magnet assemblies have been illustrated in the drawings as being separated by substantial gaps, it should be appreciated thatthis has been done solely for purposes of clarity to distinguish these surfaces from one another and that in practice, the gaps should be minimized as much as possible.

Iclaim:

l. A magnet assembly, comprising:

first and second main magnets having their respective polarities substantially oppositely directed, a first pair of opposing poles of said main magnets being located adjacent one another at an inner surface of the assembly and a second pair of opposing poles of said magnets being located adjacent one another at an outer working surface of the assembly;

first and second pole pieces contiguous with the poles of said first and second magnets, respectively, adjacent said inner surface; and

aiding magnet means disposed intermediate of said first and second pole pieces for providing a magnetomotive force additive to the magnetic flux between the first pair of opposing poles through their respective pole pieces to increase the magnetic flux produced externally of the outer working surface between the second pair of opposing poles, said pole pieces controlling the distribution of magnetic flux between the first pair of opposing poles to align it with flux produced by said aiding magnet.

2. The magnet assembly of claim 1 wherein a leakage flux is normally developed between adjacent sides of the main magnets and said aiding magnet means extends toward the outer working surface intermediate of said sides to oppose said leakage flux. 1

3. The magnet assembly of claim 1 wherein said outer working surface comprises a portion of a substantially cylindrical surface.

4. The magnet assembly of claim 3 wherein the aiding magnet means is intermediate of said first and second pole pieces in a circumferential direction.

5. The magnet assembly of claim 3 wherein said cy lindrical surface has an axis and the aiding magnet means is intermediate of said first and second pole pieces in a direction parallel thereto.

6. The magnet assembly of claim 1 including a terminal aiding magnet means comprising an aiding magnet having a pole adjacent a side of one of the pole pieces and another pole spaced therefrom, and an aiding pole piece at said other pole of the aiding magnet, said aiding magnet having its polarity directed substantially transverse to the polarity of the main magnet for providing a magnetomotive force additive to the magnetic flux between the opposite poles of the main magnet through the aiding .pole piece and the main pole piece to increase the magnetic flux produced externally of the outer working surface between the main pole and the aiding pole piece.

7. The magnet assembly of claim 6 wherein said aiding magnet means extends to the outer working surface to oppose leakage flux between the side of the main magnet adjacent thereto and the aiding pole piece.

8. The magnet assembly of claim 1 in which the configuration of the magnets is suitable for mounting within a rotatably mounted cylindrical drum having an outer surface substantially coinciding with said outer working surface and in which said outer working surface has a separation zone and a transportation zone, said main magnets having a first portion for providing a magnetic field external of the outer working surface of sufficient magnitude to attract magnetically attractable material into contact with the cylindrical drum surface in the separation zone and having a second portion for providing a magnetic field external of the outer working surface of lesser magnitude than the magnitude produced by the first portion but of sufficient magnitude to maintain the attracted material in contact with the cylindrical drum surface in the transportation zone.

9. The magnet assemblyof claim 8 in which the first portion of magnets in the separation zone extends from adjacent the separation zone of the outer working surface to adjacent a chordal plane of the outer working surface and the second portion of magnets extends a lesser amount than the first portion from adjacent the separation zone of the outer working surface toward the axis of the outer working surface.

10. The magnet assembly of claim 9 wherein a part of the first portion of magnets extends into the transportation zone and underlies a part of the second portion of magnets thereat.

11. A magnet assembly comprising:

a main magnet means having a magnet with first and second poles respectively adjacent spaced inner and outer surfaces of the assembly, and a main pole piece forming an extension of said first pole; and

aiding magnet means having an aiding magnet having one pole adjacent one side of the main pole piece and another pole spaced therefrom, and

an aiding pole piece forming an extension of said other pole of the aiding magnet for providing a low reluctance path for magnetic flux between the opposite poles of the main magnet, said aiding magnet having its polarity directed substantially transverse tothe polarity direction of the main magnet to provide a magnetomotive force additive to the magnetic flux between the aiding pole piece and the main pole piece to increase the magnetic flux between the second pole of the main magnet and the aiding pole piece produced externally of the outer working surface.

12. The magnet assembly of claim 11 wherein said aiding magnet means extends to the outer surface to oppose leakage flux between the aiding pole piece and the main magnet. 

1. A magnet assembly, comprising: first and second main magnets having their respective polarities substantially oppositely directed, a first pair of opposing poles of said main magnets being located adjacent one another at an inner surface of the assembly and a second pair of opposing poles of said magnets being located adjacent one another at an outer working surface of the assembly; first and second pole pieces contiguous with the poles of said first and second magnets, respectively, adjacent said inner surface; and aiding magnet means disposed intermediate of said first and second pole pieces for providing a magnetomotive force additive to the magnetic flux between the first pair of opposing poles through their respective pole pieces to increase the magnetic flux produced externally of the outer working surface between the second pair of opposing poles, said pole pieces controlling the distribution of magnetic flux between the first pair of opposing poles to align it with flux produced by said aiding magnet.
 2. The magnet assembly of claim 1 wherein a leakage flux is normally developed between adjacent sides of the main magnets and said aiding magnet means extends toward the outer working surface intermediate of said sides to oppose said leakage flux.
 3. The magnet assembly of claim 1 wherein said outer working surface comprises a portion of a substantially cylindrical surface.
 4. The magnet assembly of claim 3 wherein the aiding magnet means is intermediate of said first and second pole pieces in a circumferential direction.
 5. The magnet assembly of claim 3 wherein said cylindrical surface has an axis and the aiding magnet means is intermediate of said first and second pole pieces in a direction parallel thereto.
 6. The magnet assembly of claim 1 including a terminal aiding magnet means comprising an aiding magnet having a pole adjacent a side of one of the pole pieces and another pole spaced therefrom, and an aiding pole piece at said other pole of the aiding magnet, said aiding magnet having its polarity directed substantially transverse to the polarity of the main magnet for providing a magnetomotive force additive to the magnetic flux between the opposite poles of the main magnet through the aiding pole piece and the main pole piece to increase the magnetic flux produced externally of the outer working surface between the main pole and the aiding pole piece.
 7. The magnet assembly of claim 6 wherein said aiding magnet means extends to the outer working surface to oppose leakage flux between the side of the main magnet adjacent thereto and the aiding pole piece.
 8. The magnet assembly of claim 1 in which the configuration of the magnets is suitable for mounting within a rotatably mounted cylindrical drum having an outer surface substantially coinciding with said outer working surface and in which said outer working surface has a separation zone and a transportation zone, said main magnets having a first portion for providing a magnetic field external of the outer working surface of sufficient magnitude to attract magnetically attractable material into coNtact with the cylindrical drum surface in the separation zone and having a second portion for providing a magnetic field external of the outer working surface of lesser magnitude than the magnitude produced by the first portion but of sufficient magnitude to maintain the attracted material in contact with the cylindrical drum surface in the transportation zone.
 9. The magnet assembly of claim 8 in which the first portion of magnets in the separation zone extends from adjacent the separation zone of the outer working surface to adjacent a chordal plane of the outer working surface and the second portion of magnets extends a lesser amount than the first portion from adjacent the separation zone of the outer working surface toward the axis of the outer working surface.
 10. The magnet assembly of claim 9 wherein a part of the first portion of magnets extends into the transportation zone and underlies a part of the second portion of magnets thereat.
 11. A magnet assembly comprising: a main magnet means having a magnet with first and second poles respectively adjacent spaced inner and outer surfaces of the assembly, and a main pole piece forming an extension of said first pole; and aiding magnet means having an aiding magnet having one pole adjacent one side of the main pole piece and another pole spaced therefrom, and an aiding pole piece forming an extension of said other pole of the aiding magnet for providing a low reluctance path for magnetic flux between the opposite poles of the main magnet, said aiding magnet having its polarity directed substantially transverse to the polarity direction of the main magnet to provide a magnetomotive force additive to the magnetic flux between the aiding pole piece and the main pole piece to increase the magnetic flux between the second pole of the main magnet and the aiding pole piece produced externally of the outer working surface.
 12. The magnet assembly of claim 11 wherein said aiding magnet means extends to the outer surface to oppose leakage flux between the aiding pole piece and the main magnet. 